I made my unit 15 20lb rubber medicine balls. They are working very well for the Slam Ball and Wall Ball workouts. I've got 3 extras that I posted onto Ebay if anyone wants them.
25.00 US
20.00 expedited shipping. $45 is pretty cheap for a good 20lb ball. I'll also make some more by request if anyone is interested.
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&rd=1&item=7205891167&ssPage Name=STR K:MESE:IT